1. Field of the Invention
The present invention relates generally to Global Positioning System (GPS) products, and in particular, to a GPS receiver engine for use in GPS products.
2. Background Art
Global Positioning Systems (GPS) are presently being used in a wide number of military and commercial applications to enable users anywhere in the world to determine their location precisely by using a receiver to interpret signals from an array of satellites. For example, GPS is used by military aircraft and ground forces to fix locations and pinpoint targets. GPS is also used by commercial aircraft, trucking fleets, vehicles, firefighters, law enforcement organizations, farmers, fishermen, hikers and private pilots. Thus, GPS is used both for navigation and for surveillance purposes. To many recreational users, GPS has increased the safety of many recreational pursuits by providing rescue agencies with the ability to rapidly locate boaters, hikers, skiers, and others who are lost or are in trouble.
The GPS includes an array of satellites that communicate with a receiver, known as a GPS receiver, which calculates its location based on signals received from the satellites. GPS receivers are embodied in discrete end products, ranging from a simple hand-held receiver indicating the location of the receiver, to more complex end products such as car navigation systems, surveying equipment, and telecommunications base stations, among others. These GPS end products can be carried by the users or attached to the objects to be navigated or under surveillance. These GPS end products are manufactured by a number of different OEM or other manufacturers, who essentially incorporate a GPS receiver engine into the GPS end product.
FIG. 1 illustrates the electronics of a typical GPS end product. The GPS end product typically includes a GPS receiver engine provided by the GPS manufacturer on a PC board. Examples of GPS receiver engines are the "NavCore V" and the "MicroTracker" GPS receiver engines manufactured by Rockwell International Corporation, Seal Beach, Calif. The GPS end product typically also includes an OEM or local board which is made by the OEM or "local" manufacturer. Since there are also GPS manufacturers that make the GPS end product by incorporating their own GPS receiver engines, the word "local" as used throughout this disclosure includes both (1) OEM applications purchasing the GPS receiver engines from a GPS manufacturer, and (2) applications made by the same manufacturer of the GPS receiver engine.
The GPS receiver engine includes an RF circuit coupled to an antenna for receiving the signals from the satellites, a signal processing circuit coupled to a microcontroller for digital processing of the received signals, and a memory system containing GPS system software and data. The GPS system software is used to control the microcontroller to make satellite measurements and to perform the necessary calculations. Based on the signals received from the satellites and processed by the signal processing circuit, and the software instructions from the memory system, the microcontroller performs the desired calculations and outputs the navigation data (e.g., position, speed, direction, time, etc.) through a serial port to another serial port at the local board.
The local board also includes a memory system and a microcontroller. The local memory system may be used to store specific map data needed for the intended application. For example, if the GPS end product is intended for use by a vehicle in navigating through the streets of Los Angeles, the local memory system would store street names, directions and other specific map data required for such navigation. Using the map data from the local memory system, the local microcontroller translates the raw navigation data received from the GPS receiver engine into human-readable specific data, which is then output on a display associated with the GPS end product. Depending on the intended application, the GPS end product may also include a keypad or other input device that allows the user to initialize and configure the GPS end product, to enter way points for navigation, or to select different map datum. The data entered at the local board may be communicated with the GPS receiver engine via the serial port interface. A second serial port may be provided to allow the GPS end product to communicate with another separate product or device, such as a PC.
The above-described configuration suffers from the drawback that the manufacturer of the end product (also known as the local manufacturer) must provide its own microcontroller and memory system to host its application and to interface with the GPS receiver engine. As a result, two microcontrollers and two memory systems are required for each GPS end product. The cost and complexities associated with the additional microcontroller and memory system have posed problems. First, the required interface between the GPS receiver engine and the local board renders the application more prone to failures occurring during production and operation, since the increased number of components increases the likelihood of failures, and the interaction between a larger number of components results in a larger number of failure points. Second, the use of additional components increases the test time and the complexity of the tests. Third, the serial port interface between the GPS receiver engine and the local board results in communication delays between the two microcontrollers. Fourth, the resulting GPS end product would also be larger since it has additional components. Fifth, the use of an additional microcontroller and memory system increases power consumption which reduces battery life.